1. Field of the Invention
The present invention relates to a method of admitting a service request from a mobile station to an admission control device in a mobile communication system that is capable of providing a quality-guaranteed service and a quality-not-guaranteed service at the mobile station, and the admission control device.
2. Description of the Related Art
In the conventional circuit switching service, when a base station receives a request for a service from a mobile station, the base station, acting as an admission control device, determines whether the request can be admitted based on the radio resources, specifically, the number of available channels, such as the number of carriers, time slots, codes, etc., assigned to the cell formed by the base station itself, and if the number of the assigned channels is greater than a predetermined value, the base station admits the request.
In a conventional ATM (Asynchronous Transfer Mode) service, when an admission control device, such as an ATM switching system, receives a request for a service from a communication apparatus, the ATM switching system determines whether the request can be admitted based on available capacity of the path, that is, the ATM transmission channel, and on the available buffer for storing ATM cells. If the available capacity of the path and the available buffer are greater than a predetermined value, the base station admits the request.
When packet communications are performed for providing a conventional circuit switching service, because of the quality required by voice and data that share the channel, and because there are a large variety of packets, the communication quality changes after the service request is admitted.
However, as mentioned above, in the conventional circuit switching service, because admission of the request is determined based only on the assigned channels, change of the propagation quality is not considered. This conventional method is not sufficient for a mobile communication system in which the propagation quality changes frequently. In addition, in the conventional ATM service, the capacity of the path and the buffer occupied by the communications are constant after the service request is admitted. Therefore, the method used in the conventional ATM service is not suitable for a mobile communication system in which the communication rate in the cell formed by the base station changes greatly because of variation of interference and movement of the mobile stations.